Electric heating element



April 16, 1929. I F. w. MOFFAT ELECTRIC HEATING ELEMENT Filed Jan. 28, 1928 NVENTEIR w% ATIT- ENC/7% Patented Apr. 16, 19 29.

FREDEBECK W. MOFFAT, OF WESTON, ONTARIO, CANADA.

} inane ELECTRIC HEATING ELEMENT.

Application filed January 28, 1928. Serial No. 250,241.

This invention relates to electric heating elen'ients such as used in the cooking tons of electric stoves and ranges. In such elements it is known to provide a grooved disk in which coiled resistance wiring is positioned. In some cases the disk is formed of insulating material and the grooves face upwardly. In the case of what is known as a closed element the disk is formed of metal and the grooves face downwardly, the resistance wiring being retained in position by suitable insulation. In either case it is very desirable that unequal heating of the different parts of the disk be avoided, since in the case of'a metal disk this results in warping and warping is disadvantageous as it is important that the heating surface shall be and remaina plane surface and because warping tends to break up any insulation used for the heating elementsg and in the case of a disk or porcelain, or similar insulating material, unequal heating results in the cracking of the disk itself. My aim therefore is to produce a heating element less 5 subject to warping and cracking than those at present in use.

I attain my object by forming a circular disk for supporting the resistance wiring with two spiral grooves starting at substan tially diametrically opposite points, the said grooves being for the most part concentric with the rim of the disk but each jogged at substantially opposite points a distance equal to the width of a groove, whereby the outer walls of the grooves at the rim of the disk are forthe most part of even thickness. As evenness of heating of the disk from center to circumference is the ideal aimed at, I find it advantageous to increase the Width of the grooves, and thus the spacing of the convolutions of the resistance wiring, as the center is approached. The heating effect, as compared with evenly spaced convolutions is thus reduced as the center is approached.

The invention is hereinafter more fully described and illustrated in the accompanying drawings in which Fig. 1 is a plan view of the underside of the metal top of a closed element;

Fig. 2 a cross section of a complete element; and Fig. 3 a similar view of an element usin a porcelain disk.

In the drawings like numerals of reference indicate corresponding ferent figures. v

.From the drawings it will beseen that the top of the element is formed of a disk 1 having ribs 2 and 3 integral therewith, the mean thickness of each rib being approximately the same as the thickness of the disk itself. Usually, for an enclosed element, the disk and ribs will be formed of metal, but the construction and arrangement of the disk with its ribs is applicable also for use with an open heating element, in which case the disk and ribs'may be formed of the ordinary socalled porcelain employed for this purpose, or any substitute therefor.

The rib 2 is circular in form and is located as close as possible to the circumference of the disk. The ribs 3 alternate and each is formed with a plurality of alternating convolutions. The ribs 3 start and end, it will be noticed, at substantially diametrically opposite points. Ordiuarily such ribs are formed as true spirals. In my element, however, the ribs are for the most part concentric withthe rib 2, but are jogged at substantiallyv diametrically opposite points a distance equal to the width of a groove parts in the diffformed by the ribs. With this arrangement, the resistance wiring is positioned as close as possible to and almost entirely concentric with the periphery of the disk. A slight gap occurs where a heating element starts adjacent the periphery of the disk, but the passing of the other element just behind this point compensates for the incifective portion of the element. The whole purpose of the specific construction of the top is to secure an equality of heating ell'ect, andthis is materially aided by increasing the spacing of the ribs towards the center of the disk, so as to reduce the heating ellcct as the center is reached. By the mainly concentric arrangement of the ribs, and consequently the grooves, and the careful spacing of the latter, I attain the desircdequalization of the heating ellect and prevent the warping which ordinarily tends to crack the top or render the cookingsurface uneven.

lVhen the top is made of metal, the resist ance wiring requires to be secured in-position in the grooves and fully and permanent ly insulated from the metal. For this purpose I employ a series of insulating blocks 8 mainly open at their sides adjacent the disk.

The top is supported on a metal pan tilled with an insulating ceinentitious inaterial, Insulating hubs extend through the bottom of the pan close up to the under side oi the top and each hub is provided with lugs (3 by means of which it is bolted to the bottom of the pan. The ends ol? the resistance wiring are brought down through holes in these lugs and are secured to the terminal bolts 7 which pas: through holes formed in the hubs which are counter-bored to form shoulders for engagement y the heads oi the bolts. [The terminals are thus completely iusi'ilated and the ends of the resistance Wiring brought througl i for connection ivdi away from the hottest points of the element. The construction described forms a closed. heating element approximating the heating; speed of the ordinary open element. At the same time the element is durable, \VllllO the resistance Wiring and its connections are perfectly insulated and protected.

It will be noted that the outer rib 2 bevelied so that it will slightly overlap the edge oil the pan 5, thus tending to prevent liquids spilt on the top from lowing}; down over the edge and. working in between the top and the support.

When the disk made of porcelain. it is used with the grooves lacing upwardly, as shown in Fig. 3, and the resistance Wire is held down by the lips 9.

lVhen the disk is made of metal the grooves will usually be formed substantially rectangular in cross section.

What I claim as my invention is:

1. A heating element comprising a circular disk having independent ribs integral therewith of even thickness throughout their p: r -s hating a. plurality oi convolutions a; substantially diametrically opposite points and form grooves. the said ribs being; for the most with the at'oresaid circular lb each i antially diaine'trica oppoa distance equal to the r:- n'rooye. wherein; the resistance Wiring t the iined as close }T l t-i..ll)l to and almost en rely concentric with the periphcry of the disk.

A heating' element constructed as set torch in claim 1 in which the grooves adiacent the center oi the disk are wider than th se ad aceut the run.

A heating element constructed as set forth "0. claim 1 n which the disk and ribs are of approximately th same thickness.

it heating element constructed as set forth in claim 1 in which the disk and ribsv are of approximately the same thickness, and the grooves termed by the ribs (It substantially rectangular cross section.

Signed at Toronto, Canada, this th (la of January, 1928.

FREDERICK N. lllOFFii'll. 

